Corrosion-resistant rolled clad steel plate for high-temperature equipment and manufacturing method of corrosion-resistant rolled clad steel plate

Abstract

The invention discloses a corrosion-resistant rolled composite steel plate for high-temperature equipment and a manufacturing method of the corrosion-resistant rolled composite steel plate. The composite steel plate comprises a base material, a composite layer and a transition layer between the base material and the composite layer, the base material comprises the following components in percentage by weight: 0.08%-0.18% of C, 0.01%-0.6% of Si, 0.30%-0.70% of Mn, 0.009%-0.015% of Ti, 0.010%-0.015% of Als, 0.0010%-0.050% of Nb, 1.85%-3.85% of Cr, 0.5%-1.55% of Mo, 0.0007%-0.0050% of B, 0.0025%-0.0050% of N, less than or equal to 0.010% of P, less than or equal to 0.010% of S, less than or equal to 0.004% of O and the balance of Fe and other inevitable impurities. The composite steel plate interface characteristics are fully considered, the corrosion resistance of the composite stainless steel plate is guaranteed, and the composite stainless steel plate is suitable for high-temperature equipment at the working temperature of 450-530 DEG C and can be widely applied to energy industries such as thermal power, petroleum refining and chemical engineering.

Description

Technical Field

[0001] The present invention relates to corrosion-resistant steel and a manufacturing method thereof, and in particular to a corrosion-resistant rolled composite steel plate for high-temperature equipment and a manufacturing method thereof, which is suitable for high-temperature equipment with an operating temperature of 450-530°C in energy manufacturing fields such as electric power and petrochemicals. Background Art

[0002] With the rapid development of my country's economy, the demand for raw materials related to electric energy, petroleum, fertilizers, etc. is increasing. In order to improve energy production efficiency, it is imperative to make energy production and processing equipment large-scale, highly parameterized (higher temperature, higher pressure) and lightweight. This equipment upgrade demand puts higher requirements on the performance of steel plates for manufacturing equipment, that is, it requires such steel plates to have not only higher strength and hardness, but also excellent toughness and processing performance, especially better corrosion resistance. Stainless steel has very good corrosion resistance, and carbon steel has a good match of strength and toughness. If the advantages of stainless steel and carbon steel are combined, the composite material can have both high strength and high corrosion resistance. The composite steel plate of low alloy steel + various corrosion-resistant materials is a high-performance composite material. Because it has high mechanical strength and strong corrosion resistance, it is often used in crude oil processing, energy chemical industry and other industries.

[0003] The production process of traditional composite steel plates is the explosion composite process. The main problem of this production process is that when explosives are used for explosion composite, the explosion will produce a large amount of harmful gases, which will have an adverse effect on the environment, that is, this type of production process does not meet environmental protection requirements; at the same time, the bonding rate at the interface of the explosion composite steel plate is low, and sometimes cannot meet the bonding rate requirement of more than 97%. When this type of steel plate is used to manufacture various high-temperature, high-pressure, and large-scale container equipment, there will be great safety hazards. Once the composite steel plate joint is separated and the equipment fails, it will have a huge impact on the safety of life and property.

[0004] Compared with explosive composite steel plates, the bonding rate of rolled composite steel plates is greatly improved to more than 99%, and the production process is more environmentally friendly than explosive composite steel plates. Therefore, in recent years, the production scale and engineering application of rolled composite steel plates have been expanding year by year.

[0005] However, whether it is an explosive composite steel plate or a rolled composite steel plate, a certain transition layer will be produced at the interface between carbon steel and other corrosion-resistant materials. The composition of the transition layer is relatively complex, which will have an adverse effect on the strength of the carbon steel base material and the corrosion resistance of the corrosion-resistant material. Among them, especially the carbon element in the base carbon steel material enters the stainless steel at the bonding interface through the transition layer in large quantities, forming a large amount of carbides, causing intergranular corrosion of the stainless steel. When the corrosion resistance of the stainless steel is greatly affected, the corrosion-resistant material will have a greater risk of failure, especially under high temperature conditions. Once the material fails and the equipment fails, it may cause a major industrial production accident, causing casualties and huge economic losses.

[0006] Therefore, how to reasonably design the alloy composition and production process of the carbon steel base layer to minimize the negative impact of the corrosion resistance of the corrosion-resistant material caused by the diffusion of carbon elements in the base carbon steel material through the transition layer to the stainless steel due to long-term high-temperature service has become an urgent requirement to improve the comprehensive performance of the rolled composite steel plate.

[0007] Chinese patent publication number CN108231273A discloses a method for improving the interface of copper-aluminum composite materials. The invention discloses a method for improving the interface of copper-aluminum composite materials. The main technical scheme is to pre-coat or deposit graphene at the interface of copper and aluminum, and then process and composite copper, aluminum and graphene; the coating or deposition method is one of coating, electroplating, and chemical vapor deposition; the processing composite method is one of rolling composite method, extrusion composite method, and drawing composite method; the graphene is powder or film. In this technical scheme, adding graphene to the interface of copper and aluminum can ensure the interface bonding, while preventing the generation of brittle and poorly conductive intermetallic compounds at the interface, and improve the interface bonding and conductivity. Since the materials in the invention are copper and aluminum, and the main purpose of adding graphene materials at the interface is to improve the conductivity of the material. Because the properties of copper and aluminum are very different from those of low-alloy steel and stainless steel, and at the same time, carbon steel and stainless steel composite steel plates do not need to improve conductivity, the method for improving the interface performance of composite materials involved in the patent is not applicable to rolling composite steel plates of low-alloy steel and stainless steel.

[0008] Chinese patent publication number CN108239725A discloses "a high shear strength rolled composite steel plate and its manufacturing method". The high shear strength rolled composite steel plate comprises a carbon steel base layer and a stainless steel composite layer rolled and composited on the carbon steel base layer; the mass percentage of chemical elements of the carbon steel base layer is: C: 0.17% to 0.25%; Si: 0.15% to 0.40%; Mn: 1.15% to 1.50%; Mo: 0.45% to 0.60%; Ni: 0.40% to 0.70%; Al: 0.020 to 0.040%; Ca: 0.0010 to 0.0030%; the remainder is Fe and other inevitable impurities. The high shear strength rolled composite steel plate has a tensile strength of 570 to 690 MPa at room temperature, a yield strength of ≥365 MPa at room temperature, a shear strength of ≥350 MPa, and an elongation of ≥20%. In this patent, the inventor achieved high shear strength performance of the composite steel plate by controlling the microstructure ratio of the carbon steel material. However, the invention material did not mention the control of the structure and precipitation at the interface.

[0009] Chinese patent publication number CN108085585A discloses "a high-strength corrosion-resistant composite patterned steel and its manufacturing method". In the rolled composite steel plate, the base layer is carbon steel, the composite layer is austenitic stainless steel, and the thickness of the composite steel plate is no more than 10 mm. The inventor directly assembles the carbon steel slab and the austenitic stainless steel slab, and adopts a coiling process after hot rolling to finally obtain a rolled composite plate coil. The target steel type of this invention patent is a hot-rolled composite plate coil product with a thickness of less than 10 mm, and its working temperature is generally room temperature. The invention does not involve the influence of high temperature working conditions on the corrosion resistance of the composite material at the interface of the composite material.

[0010] Based on the above patents, the existing rolled composite steel plate technology, especially the carbon steel and stainless steel composite plate production technology, has little consideration for the transition layer at the interface between the base and the composite material, especially the diffusion of alloy elements, especially carbon elements, in the carbon steel material to the interface, which may cause a significant decrease in the corrosion resistance of the stainless steel, and ultimately there is a hidden danger of material failure, which is almost not involved. Therefore, in the technical solutions of the disclosed patents, basically no targeted measures have been taken to reduce the possibility of weakening the corrosion resistance of the stainless steel due to the precipitation of carbides at the grain boundaries of the stainless steel at the interface of the composite material. In fact, in the chemical and energy industries, in many cases, the operating temperature of the composite steel plate manufacturing equipment is in the range of 450-530℃. If it is operated at such a high temperature for a long time, the elements at the material interface may diffuse again, especially the carbon elements on the carbon steel side diffuse to the stainless steel composite layer, which will form more and larger carbides, which will further reduce the corrosion resistance of the stainless steel and form an accident hazard. Summary of the invention

[0011] The purpose of the present invention is to provide a corrosion-resistant rolled composite steel plate for high-temperature equipment and a manufacturing method thereof, which fully considers the interface characteristics of the composite steel plate and can ensure the corrosion resistance of the composite stainless steel. It is suitable for high-temperature equipment with an operating temperature of 450 to 530°C and can be widely used in energy industries such as thermal power, petroleum refining, and chemical industry.

[0012] To achieve the above object, the technical solution of the present invention is:

[0013] The composite steel plate of the present invention forms a large number of MC (M represents one or more of Cr, Mo, Nb, Ti) precipitation phases with fine and dispersed distribution and stable high-temperature performance in the base carbon steel. These stable carbide precipitation phases can fix the carbon element in the steel in the base carbon steel, thereby avoiding the diffusion and migration of the carbon element in the carbon steel to the interface of the rolled composite steel plate under high-temperature working conditions of 450°C to 530°C, resulting in an increase in the carbon element concentration in the stainless steel near the interface, and a large number of carbide precipitation phases are generated at the stainless steel grain boundaries, inducing intergranular corrosion, and ultimately weakening or even losing the anti-corrosion function of the composite material.

[0014] Specifically, the corrosion-resistant rolled composite steel plate for high-temperature equipment of the present invention comprises a substrate, a composite layer and a transition layer between the substrate and the composite layer; the weight percentage of the components of the substrate is: C: 0.08% to 0.18%, Si: 0.01% to 0.6%, Mn: 0.30% to 0.70%, Ti: 0.009% to 0.015%, Als: 0.010% to 0.015%, Nb: 0.0010% to 0.050%, Cr: 1.85% to 3.85%, Mo: 0.5% to 1.55%, B: 0.0007% to 0.0050%, N: 0.0025% to 0.0050%, P≤0.010%, S≤0.010%, O≤0.004%, and the balance comprises Fe and other inevitable impurities;

[0015] The surface microstructure of the composite steel plate substrate is 90-95% bainite + 5-10% martensite + MC precipitation phase, and the central microstructure of the substrate is 90-95% bainite + 0-5% martensite + 0-5% ferrite + MC precipitation phase; wherein M represents one or more of Cr, Mo, Nb, and Ti, the average major axis length of the MC precipitation phase is less than 400 nm, and the volume density of the MC precipitation phase with a major axis length less than 400 nm is greater than 3.0×10 4 Pieces / mm 3 ;

[0016] The composite steel plate is made of stainless steel, and its microstructure contains MC precipitated phase, wherein M represents one or more of Cr, Mo, Nb, and Ti, and the average major axis length of the MC precipitated phase is less than 700 nm, and the volume density of the MC precipitated phase is less than 1.0×10 4 Pieces / mm 3 ;

[0017] Preferably, the stainless steel is austenitic stainless steel, ferritic stainless steel, duplex stainless steel or super stainless steel.

[0018] Furthermore, the balance of the composite steel plate substrate composition is Fe and other inevitable impurities.

[0019] Furthermore, the composite steel plate substrate composition also contains at least one of the following chemical elements: 0<Ca≤0.0055%, 0<Ni≤0.65%, 0<Cu≤0.55%.

[0020] Preferably, the number ratio of MC precipitates with a major axis length of less than 400 nm in the composite steel plate substrate is greater than 50%.

[0021] Preferably, the number ratio of MC precipitates with a major axis length of less than 700 nm in the composite steel plate composite layer to all MC precipitates is greater than 50%.

[0022] Furthermore, the microstructure of the composite steel plate layer may also contain a very small amount of σ phase, with the σ phase ratio being ≤1.5%. Preferably, the σ phase ratio near the transition layer is ≤0.5%.

[0023] Preferably, the thickness of the composite steel plate substrate is ≥6 mm, and the thickness of the composite layer is ≥2 mm; preferably, the thickness of the transition layer is ≤250 μm.

[0024] The yield strength of the rolled composite steel plate substrate of the present invention is ≥455MPa, the tensile strength is ≥535MPa, the cross-sectional shrinkage is ≥65%, the elongation is ≥18%, the -40°C impact absorption energy is ≥120J, and the -60°C impact absorption capacity is ≥70J; the grain size grade of the substrate is not less than grade 7.0; and the shear strength of the rolled composite steel plate is ≥330MPa.

[0025] In the composition design of the composite steel plate substrate of the present invention:

[0026] C: C is an important alloying element. In order to make the carbon steel plate have appropriate strength, it is necessary to control the mass percentage of C in the steel to be greater than or equal to 0.08%. At the same time, in order to improve the welding performance of the substrate carbon steel material, it is necessary to control the upper limit of the C content in the carbon steel. In addition, if the carbon content in the carbon steel substrate is high, due to the difference in the carbon concentration gradient of the two materials, a large-scale carbon migration will occur at the interface between the substrate and the stainless steel composite material, causing intergranular corrosion of the stainless steel. Therefore, its upper limit is controlled to 0.18%. In addition, controlling the appropriate carbon content can form a large amount of dispersed nano-scale carbides in the steel through the combination of ingredients and processes, and can also play a precipitation strengthening effect to improve the strength of the substrate carbon steel. Based on this, the present invention controls the C content to 0.08-0.18%.

[0027] Si: Si is also a commonly used strengthening element in low alloy steel. Adding a certain amount of Si to steel can improve the strength of steel. At the same time, Si also has a deoxidation function. During the smelting process, it can play an auxiliary deoxidation role. Most of the SiO2 products formed after deoxidation enter the steel slag and are removed, which will not affect the performance of the steel. In addition, adding a certain amount of Si to steel can reduce the solubility of carbon in austenite, thereby promoting carbon precipitation, promoting the formation of MC precipitation phase, fixing carbon in steel, and preventing large-scale diffusion of carbon to the interface. Therefore, a certain amount of Si needs to be added to the steel. However, when the Si content is too high, the welding performance of the steel will be reduced. In addition, the binding ability of Si with oxygen is stronger than that of iron with oxygen. It is easy to generate low-melting silicates during welding, increase the fluidity of slag and molten metal, cause splashing, and affect the quality of the welded joint. Therefore, controlling the content of Si within a certain range is helpful to improve the welding forming performance of steel. Therefore, the present invention controls the Si content to 0.01-0.6%.

[0028] Mn: Mn is also an important strengthening element, which can effectively improve the strength of the base steel plate. In addition, the Mn element is an effective austenite stabilizing element. Adding a certain amount of Mn elements can increase the hardenability of steel. Therefore, in order to ensure the strength of steel, the lower limit of Mn is 0.30%. However, the Mn element is very easy to produce center segregation in steel. Excessive addition of Mn elements will cause serious segregation at the center of the thickness of the steel plate and reduce the low-temperature toughness of the core of the steel plate. Therefore, the upper limit of the Mn content is limited to 0.70%. Based on this, the present invention controls the Mn content to 0.30% to 0.70%.

[0029] Ti: Ti, as a deoxidizing element, participates in the deoxidation reaction during the smelting process, which facilitates the precise control of the oxygen level of molten steel. After Ti deoxidation, Ti2O3 particles can be formed to promote the formation of intracrystalline ferrite and improve the low-temperature impact toughness of steel. At the same time, Ti is also a strong carbide-forming element and nitride-forming element. In the present invention, adding an appropriate amount of Ti element can, on the one hand, form a stable MC precipitation phase in the steel, fix the carbon element in the substrate, and prevent it from diffusing to the interface of the composite material. In addition, part of the Ti element participates in fixing the free N element in the steel to form a TiN precipitation phase, which can prevent the growth of austenite grains, refine the grains, and simultaneously improve the strength and toughness of the steel plate. After Ti fixes part of the free nitrogen element, it helps to avoid the combination of B element and N element to form a BN precipitation phase, thereby ensuring that the B element in the steel exists in the steel in a free state, improving the hardenability of the steel, and ensuring that the steel plate has excellent strength properties. In the alloy system of the present invention, when the Ti content is lower than 0.009%, the amount of TiN and Ti2O3 formed is relatively small, and the pinning effect on austenite grains is weakened, so the Ti content in the steel is controlled to be not less than 0.009%. However, when the Ti content in the steel is too high, the particle size of the TiN and Ti2O3 formed becomes larger, so that these precipitated phases no longer have the ability to hinder the growth of austenite and form intracrystalline ferrite, but will easily become the source of crack initiation, reducing the low-temperature impact toughness of the steel, so the upper limit of Ti is 0.015%. Based on this, the present invention controls the Ti content to 0.009-0.015%.

[0030] Cr: Adding an appropriate amount of Cr can improve the hardenability of the steel plate, ensure the uniformity of the performance on the thickness section after the thick steel plate is quenched, and especially ensure that the core of the steel plate has high strength and toughness. Adding Cr to the steel can improve the oxidation resistance of the steel plate when working at a high temperature of 450-530°C. In addition, as a strong carbide-forming element, the Cr element in the steel can combine with the free carbon in the steel plate to form a stable MC carbide, fix the free carbon in the carbon steel, and avoid the diffusion of carbon into the interface position, affecting the corrosion resistance of the composite material. When the Cr content in the steel is low, its effect on the hardenability of the thick steel plate is weakened. At the same time, the formation of stable carbides is reduced, and the fixation effect on free carbon is weakened. Therefore, in the present invention, the Cr content is not less than 1.85%. However, when the Cr content is high, the anti-temper embrittlement performance of the steel plate will be reduced, which is not conducive to the long-term operation of the steel plate at high temperature. Therefore, the upper limit of the Cr element is set to 3.85%. Based on the above reasons, the present invention controls the Cr content to 1.85-3.85%.

[0031] Mo: Mo is a strong carbide-forming element. Mo can improve the high-temperature creep strength of steel plates by forming a composite solid solution with interstitial elements such as carbon and nitrogen. Adding an appropriate amount of Mo can also form a small, stable MC carbide precipitation phase, which can achieve the effect of precipitation strengthening on the one hand, and on the other hand, can also fix the free carbon in carbon steel. When the Mo content in the alloy system is lower than 0.50, the carbide density is low, and the precipitation strengthening and carbon fixation effects are reduced. However, when the Mo content in the steel is high, the precipitation phase is easy to mature and the size becomes larger, and its precipitation strengthening effect will also be weakened. Based on this, the present invention controls the Mo content to 0.50-1.55%.

[0032] Acid-soluble Als: Al is an important deoxidizing element that forms aluminum oxide inclusions; moreover, the Al element can combine with the N element in the steel to form an AlN precipitation phase, which reduces the content of free N elements in the steel, thereby avoiding the combination of the B element in the steel with the N element, promoting the increase of the free B element content in the steel, improving the hardenability of the steel, and helping to improve the strength performance of the steel plate. However, when the acid-soluble aluminum content in the steel is too high, the size of its deoxidation product aluminum oxide will become larger, and because the aluminum oxide inclusions have a strong adsorption capacity, it will lead to the formation of large-sized aluminum oxide clusters, which will clog the water inlet during the steelmaking process and affect the casting process of the molten steel. If these large-sized clustered inclusions enter the steel plate, it will cause the inclusion rating and flaw detection of the steel plate to fail. Therefore, the present invention controls the acid-soluble Als content to 0.010-0.015%.

[0033] Nb: Nb is a strong carbide-forming element. The Nb element can combine with the carbon element in the steel to form a MC precipitation phase, stabilize the carbon element in the steel, and prevent the carbon element from diffusing to the interface. At the same time, adding an appropriate amount of Nb element can increase the recrystallization temperature of the steel. After the steel is recrystallized and rolled in the austenite region, the austenite grains will not grow rapidly, and the strength and toughness of the fine-grained steel are higher. However, when the Nb element content in the steel is too high, the size of the formed MC precipitation phase will be larger, which will reduce the toughness of the steel plate and deteriorate the toughness of the welding heat affected zone. Therefore, the present invention controls the Nb content to 0.0010-0.050%.

[0034] B: Adding an appropriate amount of B element is to make up for the fact that after the free carbon in the steel is fixed by stable carbides, the solid solution carbon content in the steel is reduced, resulting in a decrease in the strength performance of the steel plate. If the B element in the steel exists in a free state, some of the B will preferentially occupy the grain boundary position, thereby improving the hardenability of the steel plate. The premise for its function is that B must exist in the steel in a free state. Therefore, in order to prevent the B in the steel from combining with the oxygen and nitrogen elements to form boron oxide and boron nitride, the oxygen content and nitrogen content in the steel must be controlled, which is also the key point in the design of the alloy composition. However, it should be noted that after adding excessive B to the steel, too much B is prone to form a large amount of segregation at the grain boundary, which is detrimental to the toughness of the steel. Therefore, the present invention controls the B content to 0.0007-0.0050%.

[0035] N: When designing the alloy composition of the present invention, appropriate amounts of Ti and Al elements are added. These two elements can form TiN and AlN precipitation phases with the N element in the steel. When these precipitation phases are fine and dispersed, they can refine the austenite grains, thereby improving the strength and toughness of the steel plate. However, when the N content in the steel is too high, the excess N element will combine with the B element in the steel to generate BN, consume the free B element in the steel, and reduce the effect of the B element on improving the strength of the steel plate. At the same time, too much N element will have an adverse effect on the toughness of the steel, especially when the solid solution N content exceeds 0.005%, the low-temperature toughness of the steel plate will be significantly reduced. Therefore, the present invention controls the N content to 0.0025-0.0050%.

[0036] Preferably, in the rolled composite steel plate substrate for high temperature equipment of the present invention, it further contains at least one of the following chemical elements: 0<Ca≤0.0055%, 0<Ni≤0.65%, 0<Cu≤0.55%.

[0037] In the above technical solution of the present invention, the elements Ca, Ni and Cu can further improve the performance of the steel plate for high temperature equipment of the present invention.

[0038] Ca: Ca is a strong deoxidizing element. Adding an appropriate amount of calcium can control the oxygen content in the steel, thereby preventing the oxidation of the B element. However, when the Ca content in the steel exceeds 0.0055%, large inclusions of calcium oxide and calcium sulfide are easily formed in the steel, which is detrimental to the toughness of the steel. Therefore, the present invention controls the Ca content to 0<Ca≤0.0055%.

[0039] Ni: Ni is a typical austenite stabilizing element, which can significantly improve the hardenability of the steel plate, and can also improve the low temperature toughness of the steel plate. However, the price of Ni is relatively high. Considering the production cost of steel, it is not appropriate to add excessive Ni to the steel. Therefore, the present invention controls the Ni content to 0<Ni≤0.65%.

[0040] Cu: In the rolled composite steel plate substrate for high temperature equipment of the present invention, adding an appropriate amount of Cu element helps to improve the strength of the steel and improve the corrosion resistance of the steel. However, when the Cu content added to the steel is too high, the steel plate is prone to high temperature brittleness at high temperatures. Therefore, the present invention controls the Cu content to 0<Cu≤0.55%.

[0041] It should be noted that the addition of the above-mentioned Ca, Ni and Cu elements will increase the cost of the material. Taking into account the performance and cost control, in the technical solution of the present invention, at least one of the above-mentioned elements can be preferably added.

[0042] Inevitable impurities exist in the composite steel plate substrate of the present invention, P≤0.010%, S≤0.010%, O≤0.004%.

[0043] P, S and O are all impurity elements in steel. When technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in steel should be reduced as much as possible.

[0044] P: P is a harmful element for most steel plates. The main reason is that P is very easy to segregate to the grain boundary, reducing the bonding force between atoms at the grain boundary, causing the temper brittleness of the steel plate, especially when the steel plate is working at high temperature, the temper brittleness of P will be aggravated. Therefore, in the rolled composite steel plate substrate for high temperature equipment described in the present invention, the mass percentage of P is controlled to P≤0.010%.

[0045] S: The S element in steel is very easy to combine with the Mn element in steel to form MnS inclusions. The higher the S content, the larger the size of the MnS formed, which is not good for the strength and toughness of the steel plate. At the same time, when the S content is too high, it will cause the center segregation of the slab and easily cause hot cracks. Therefore, in the rolled composite steel plate substrate for high-temperature equipment described in the present invention, the mass percentage of the S element is controlled to S≤0.010%.

[0046] O: The oxygen element in steel basically exists in the form of oxides. When the content of O in steel is too high, it means that there are too many oxides in the steel, and large inclusions may exist, which affects the strength and toughness of the steel plate. Therefore, in the rolled composite steel plate substrate for high-temperature equipment described in the present invention, the mass percentage of O is controlled to O≤0.004%.

[0047] The surface structure of the composite steel plate substrate of the present invention is 90-95% bainite structure and 5-10% martensite structure, and the central microstructure is 90-95% bainite (B) and 0-5% martensite (M) structure + 0-5% ferrite (F) structure. In order to ensure that the tensile strength and low-temperature impact performance of the composite steel plate substrate meet the requirements, it is necessary to ensure that 90-95% of the structure of the surface and center of the steel plate thickness is bainite structure; 5-10% martensite structure on the surface of the steel plate can further improve the strength of the surface steel plate to compensate for the reduction in strength after part of the free carbon elements are converted into carbides during subsequent high-temperature service. 0-5% ferrite in the central microstructure is beneficial to improve its low-temperature impact toughness to compensate for the problem of reduced toughness in the center of the plate thickness due to segregation.

[0048] The substrate of the present invention has a stable MC precipitation phase, wherein M represents one or more of Cr, Mo, Nb, and Ti, and the average major axis length of the MC precipitation phase is less than 400nm. Since the precipitate phase has a large size, it will have an adverse effect on the mechanical properties of the steel plate, especially the low-temperature impact toughness. Therefore, in the present invention, the average major axis length of the MC precipitation phase in the steel plate needs to be controlled to be less than 400nm. In the substrate of the present invention, a carbide precipitation phase with a smaller size is formed as much as possible to ensure that while the carbon fixation effect of the carbide is fully exerted, the mechanical properties of the steel plate will not be adversely affected by the precipitation of the carbide. Therefore, the MC precipitation phase with a major axis length of less than 400nm is limited to a number ratio of more than 50% of the total MC precipitation phase.

[0049] Preferably, the volume density of the MC precipitated phase with a major axis length less than 400 nm in the substrate is greater than 3.0×10 4 Pieces / mm 3 The purpose of forming MC precipitation phase in steel is to fix the free carbon element in the steel. Therefore, in the present invention, it is necessary to ensure that the volume density of MC with a major axis length of less than 400 nm is greater than 3.0×10 4 Pieces / mm 3 Only in this way can the carbon element in the steel be effectively controlled and the large-scale diffusion of free carbon elements to the stainless steel side be avoided.

[0050] Preferably, the MC precipitate phase with a major axis length of less than 400nm in the substrate accounts for more than 50% of the total MC precipitate phase. In the present invention, the "volume density" of the MC precipitate phase is measured according to the method described in the YB / T 5320-2006 standard. In the present invention, a carbide precipitate phase with a smaller size is formed as much as possible to ensure that the mechanical properties of the steel plate will not be adversely affected by the precipitation of carbides while fully exerting the carbon fixation effect of carbides. Therefore, the MC precipitate phase with a major axis length of less than 400nm accounts for more than 50% of the total MC precipitate phase.

[0051] The composite steel plate composite material of the present invention has a stable MC precipitation phase, wherein M represents one or more of Cr, Mo, Nb, and Ti, and the average major axis length of the MC precipitation phase is less than 700nm. The larger the size of the carbide in the composite material, the greater the impact on the corrosion resistance of the stainless steel. Therefore, it is hoped that the size of the carbide precipitation phase in the composite material is as small as possible. However, in the production process of the composite material and the rolled composite steel plate, some carbide precipitation phases will inevitably be generated. In order to ensure the corrosion resistance of the rolled composite steel plate, the present invention requires that the average major axis length of the MC precipitation phase in the composite material is less than 700nm.

[0052] The volume density of the MC precipitated phase in the composite material of the present invention is less than 1.0×10 4 Pieces / mm 3 From the perspective of controlling the amount of carbide precipitation phase in the composite material, it is hoped that the amount of carbides is as small as possible, that is, the smaller the volume density is, the better. However, some carbides will inevitably form during the heat treatment of the composite steel plate. The volume density of carbides is controlled to be less than 1.0×10 4 Pieces / mm 3 It can ensure the excellent corrosion resistance of the composite material.

[0053] Preferably, in the composite material of the present invention, the MC precipitate phase with a major axis length less than 700nm accounts for more than 50% of the total MC precipitate phase. In the present invention, the "volume density" of the MC precipitate phase is measured according to the method described in the YB / T 5320-2006 standard. In order to reduce the carbide precipitate phase in the composite material as much as possible to increase the corrosion resistance of the composite material, the size and number of the MC precipitate phase are limited in the present invention, that is, the MC precipitate phase with a major axis length less than 700nm accounts for more than 50% of the total MC precipitate phase. When the number and size of the carbide precipitate phase exceed the limit range, the corrosion resistance of the composite material will be greatly reduced, affecting the safe service performance of the rolled composite steel plate.

[0054] The composite layer of the present invention is stainless steel (including austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, super stainless steel and other stainless steel products). The σ phase in stainless steel is a metal phase with very high hardness and very low plasticity. When it exists in stainless steel, especially when it precipitates along the grain boundary, it will have a great impact on the plasticity of the steel, resulting in a significant reduction in the impact toughness of the steel. Therefore, the σ phase ratio of stainless steel is ≤1.5%, especially the σ phase ratio near the bonding interface (transition layer) is ≤0.5%.

[0055] The present invention also provides a method for manufacturing the rolled composite steel plate for high temperature equipment, which comprises the following steps:

[0056] 1) Smelting and casting, preparation of base material and composite casting billet

[0057] The above components are smelted and cast into a base material ingot, and deoxidizers Si+Mn, Al, and Ti alloys are sequentially added to the molten steel during the smelting process for deoxidation, wherein Si+Mn and Al are first added for pre-deoxidation, and the oxygen level of the molten steel is 0.0020% to 0.0075% after the pre-deoxidation, and then Ti is added for final deoxidation; after the deoxidation, B element is added, and then other alloys are added, and after homogenization, casting is performed using the top pouring method; at the same time, a stainless steel composite ingot is obtained;

[0058] 2) Assembly

[0059] The substrate and the composite casting blank are subjected to surface treatment, and then stacked, and the four sides of the stacked composite blank are welded and sealed, vacuumed, and sealed again; preferably, after vacuuming, the vacuum degree is 8 to 60 Pa;

[0060] 3) Composite slab rolling

[0061] The composite slab is heated to 1080-1250°C, and then rolled in two stages, the total reduction rate of the slab in the first stage is not less than 60%, the total reduction rate in the second stage is not less than 20%, the reduction rate of the last pass is 8-18%, and the total cumulative reduction rate of the two-stage rolling is not less than 80%; the final rolling temperature is above 880°C;

[0062] 4) Heat treatment: quenching and tempering the composite steel plate.

[0063] Preferably, in step 2), the surfaces of the substrate and the composite ingot are processed to ensure that there are no obvious surface defects such as oil stains, slag inclusions, cracks, etc. on the ingot surface, and at the same time, the roughness of the processed surface of the ingot needs to be ensured to be no greater than 2.0 Ra.

[0064] Preferably, in step 4), the quenching temperature is 945-985°C, the quenching holding time is T1=(1-1.2)H, and after the holding is completed, the steel plate is taken out of the furnace and cooled to room temperature with water, wherein T1 is in min, and H is the thickness of the steel plate in mm.

[0065] Preferably, in step 4), the tempering temperature is 690-735°C, the tempering holding time is T2=(1-1.5)H, and after the holding is completed, the steel plate is taken out of the furnace and cooled to room temperature with water, wherein T2 is in min, and H is the thickness of the steel plate in mm.

[0066] In the manufacturing method of the present invention:

[0067] A large amount of uniformly dispersed nano-scale MC precipitation phases need to be generated in the composite steel plate substrate of the present invention, and the MC precipitation phase is used to fix the free carbon element in the carbon steel substrate to prevent the carbon element from diffusing in large quantities to the interface between the substrate and the composite material, thereby causing the stainless steel to form carbides and reducing its corrosion resistance, thereby improving the service safety performance of the rolled composite steel plate for high-temperature equipment. However, the free carbon in the steel is a major strengthening element of the carbon steel substrate. When most of the free carbon elements are fixed in the form of MC, the strength of the carbon steel will be reduced. In order to compensate for the strength loss after the carbon elements are fixed. It is necessary to add the B element to improve the hardenability of the steel plate. The hardenability of the B element mainly works through the distribution of free B at the grain boundary. Since the B element is an extremely active element, on the one hand, it can combine with the oxygen element in the molten steel to form boron oxide; on the other hand, the boron element is also easy to combine with the N element to form boron carbide. For this reason, in the technical solution of the present invention, the deoxidation sequence of the molten steel and the timing of adding the B element are specially designed. That is, during deoxidation, Si and Mn are used for pre-deoxidation, and most of silicon oxide and manganese oxide will float to the top slag. Using strong deoxidizer Al for deoxidation can more accurately control the oxygen level (determined according to the method for measuring oxygen content in molten steel recorded in ISO 14284:1996 standard) at 0.0020% to 0.0075%, and then Ti is used for final deoxidation to form a large amount of Ti oxide. At the same time, the added Ti can combine with the free nitrogen element in the steel to form TiN. That is, the addition of Ti element will further reduce the free oxygen concentration in the steel. Within a certain oxygen position range (0.0020-0.0075%), the size of the Ti2O3 inclusions formed after deoxidation is appropriate (2-5μm), which is conducive to the formation of part of the needle-shaped ferrite structure during solidification and subsequent phase transformation, and improves the toughness of the steel plate. In addition, Ti element can also combine with N element in steel to generate part of TiN, which can reduce the adverse effect of solid solution nitrogen on the toughness of steel on the one hand, and on the other hand, TiN can precipitate at high temperature during solidification, play a role in pinning the growth of austenite, and refine the original austenite grains. When the oxygen and titanium elements in the steel are controlled in place, an appropriate amount of B element is added, thereby ensuring that the added B element is mainly present in the steel in a free state, ensuring that the base steel plate has a high hardenability, and can significantly improve the strength of the steel plate. Most importantly, through the above-mentioned deoxidizer addition sequence and oxygen position control technology, a large amount of uniformly dispersed, fine (2-5μm), spherical Ti2O3 oxides can be formed in the steel, which can serve as nucleation cores for the subsequent precipitation of carbides. Since these carbide nucleation cores are uniformly dispersed in the steel, it can be ensured that the precipitated carbides are also uniformly dispersed in the steel, while ensuring that their number is large and their size is small, and will not have an adverse effect on the mechanical properties of the substrate.

[0068] In step 2), the surfaces of the substrate and the composite ingot are processed to ensure that there are no obvious surface defects such as oil stains, slag inclusions, cracks, etc. on the surface of the ingot, and at the same time, the roughness of the processed surface of the ingot is required to be no greater than 2.0Ra. After the vacuum is evacuated, the vacuum degree is 8-60Pa, so as to ensure the rolling effect of the composite slab.

[0069] In step 3), the composite slab is heated to 1080-1250°C for rolling because: when the heating temperature is less than 1080°C, the carbides and nitrides in the base material ingot cannot be completely dissolved, which will reduce the pinning effect of the carbides on the austenite grains during the rolling process; at the same time, within this temperature range, it is conducive to the homogenization of the austenite of the composite material, and the carbides in the composite material are also completely dissolved. When the heating temperature of the ingot is higher than 1250°C, it is easy to cause the rapid growth of the austenite grains of the base material and the composite material, which will damage the mechanical properties of the steel.

[0070] In addition, the total reduction rate of the slab in the first stage of rolling is not less than 60%, the total reduction rate in the second stage of rolling is not less than 20%, the reduction rate of the last pass is 8-18%, the total cumulative reduction rate of rolling is not less than 80%, and the final rolling temperature is above 880°C.

[0071] Through the first stage of high-temperature and high-reduction rolling, the material can be fully recrystallized during the rolling deformation process, the austenite grains can be continuously refined, and the formation of larger austenite grains in the steel can be inhibited, thereby improving the low-temperature toughness of the steel. When the total reduction rate in the first stage is less than 60%, the austenite grain size in the steel is larger, which is not conducive to the strength and toughness indicators of the steel plate.

[0072] The total reduction rate of the second stage rolling is not less than 20%, which can further promote the refinement of austenite grains. The reduction rate of the final rolling pass is 8-18%, which can increase the dislocation density in the steel and ensure the strength of the steel plate. When the reduction rate is lower than 8%, the dislocation density is low, which is not conducive to strength improvement. When the reduction rate is higher than 18%, the rolling torque is too large, which is not conducive to the rolling equipment. When the final rolling temperature is lower than 880℃, the deformation resistance of the steel plate increases, and it is difficult to ensure a larger final rolling reduction rate.

[0073] During the quenching process, when the quenching temperature is lower than 945°C, it takes a long time for the austenite of the steel to be homogenized, which will reduce the heat treatment efficiency; if the quenching temperature of the steel is higher than 985°C, part of the austenite in the carbon steel tends to grow and is easy to form a mixed crystal structure, which is not conducive to the uniformity of the steel structure. Accordingly, when the holding time T1 of the steel at the quenching temperature is less than 1H, it cannot be fully austenitized, and when the quenching holding time T1 of the steel exceeds 1.2H, it will exceed the time required for the steel to be austenitized, which will reduce the efficiency of the quenching process.

[0074] During the tempering process, when the tempering temperature of the steel is lower than 690℃, a longer tempering time is required to remove the residual quenching stress in the steel, which will reduce the tempering efficiency and the formation rate of MC precipitation phase in carbon steel will be slower; when the tempering temperature of the steel is higher than 735℃, the MC precipitation phase in the steel is prone to Ostwald coarsening and aggregation and growth, which is not conducive to the formation of fine and dispersed MC precipitation phase in the steel. Correspondingly, when the tempering holding time T2 is lower than 1.0H, the quenching stress of the steel tends to be unable to be completely removed, and when the tempering holding time T2 is higher than 1.5H, the MC precipitation phase in the steel is prone to coarsening and will reduce the production efficiency of the tempering process.

[0075] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0076] The present invention forms a large number of dispersedly distributed nano-scale MC (M represents one or more of Cr, Mo, Nb, and Ti) precipitation phases in the steel by using fine and dispersed spherical (2-5 μm) Ti2O3 oxides formed in the steel as nucleation cores of MC carbide precipitation phases, thereby fixing free carbon and carbon elements in the carbon steel, preventing the carbon elements from diffusing and aggregating at the composite interface (transition layer), reducing the precipitation of carbides at the grain boundaries of stainless steel, and ensuring the corrosion resistance of the composite rolled steel plate. In particular, when the rolled composite steel plate is applied to high-temperature equipment, under high-temperature working conditions of 450° C. to 530° C., the high-melting-point Ti2O3 oxide (melting point is 2130° C.) can still stably exist in the steel and continue to play a role as the precipitation core of MC carbides. That is, some of the free carbon elements in the steel can still react with the alloy elements in the steel with Ti2O3 oxide as the nucleation core to form fine MC carbides, thereby further fixing the carbon elements, ensuring that the carbon elements in the carbon steel do not diffuse to the interface, and protecting the corrosion resistance of the rolled composite steel plate under long-term high-temperature service.

[0077] In addition, for the smelting process in the production process of low-alloy high-strength steel, the current typical smelting technology is aluminum deoxidation killed steel, that is, the oxygen content in the steel is controlled within the target range through aluminum deoxidation. Its characteristics are high deoxidation efficiency, but it is easy to form larger and more Al2O3 inclusions in the steel. Such inclusions are easy to gather in the steel to form inclusion clusters, resulting in unqualified flaw detection, mechanical properties or inclusion rating of the steel plate; at the same time, most Al2O3 inclusions are irregular polyhedral block morphology, which cannot serve as carbide nucleation cores to promote the dispersion and uniform distribution of carbides. Therefore, in aluminum killed steel, carbide precipitation phases tend to gather at grain boundaries and have large sizes, which will have adverse effects on both the conventional properties and high temperature properties of the steel.

[0078] The present invention optimizes the production process, that is, controls the type of deoxidizer, the deoxidation sequence and the amount of deoxidizer added during the steel smelting process, so that the type of deoxidation product in the steel can be controlled to be a spherical (2-5μm) Ti2O3 oxide with a high melting point and fine dispersion distribution. Compared with the Al2O3 inclusions formed in the traditional aluminum-killed steel, this type of oxide is not easy to aggregate and grow, has no edges and corners, is harmless to the flaw detection and mechanical properties of the steel plate, and can optimize the organization type of the steel plate; refines the austenite grains through TiN precipitation; reduces the oxidation and nitridation amounts of the B element by designing the addition sequence of the steel alloy, can fully utilize the added B element, maximize the improvement of the hardenability of the steel plate, refine the grains, and ensure that the steel plate has high strength and excellent low-temperature toughness.

[0079] In addition, through the control of the smelting process, especially through the control of the type of deoxidizer, the deoxidation sequence and the amount of deoxidizer added, the fine and dispersed spherical (2-5μm) Ti2O3 oxide formed in the steel can serve as the nucleation core of the MC carbide precipitation phase. Combined with the design of the alloy composition optimization and the design of the heat treatment process, a large number of dispersed and distributed nano-scale MC (M represents one or more of Cr, Mo, Nb, Ti) precipitation phases can be formed in the steel, which fixes the free carbon carbon elements in the carbon steel, avoids the diffusion and aggregation of carbon elements to the composite interface (transition layer), reduces the precipitation of stainless steel grain boundary carbides, and ensures the corrosion resistance of the composite rolled steel plate. In particular, when the rolled composite steel plate is used for high-temperature equipment, under the high temperature working conditions of 450-530°C, the high melting point Ti2O3 oxide (melting point is 2130°C) formed by controlling the smelting process can still stably exist in the steel, and continue to play a role as the precipitation core of MC carbides. That is, some of the free carbon elements in the steel can still react with the alloy elements in the steel with Ti2O3 oxide as the nucleation core to form fine MC carbides, thereby further fixing the carbon elements, ensuring that the carbon elements in the carbon steel do not diffuse to the interface, and protecting the corrosion resistance of the rolled composite steel plate under long-term high-temperature service.

[0080] The rolled composite steel plate for high-temperature equipment produced by the present invention has excellent corrosion resistance and can be effectively used in the energy and chemical industry as a manufacturing material for 450-530°C high-temperature reaction vessels. It has very important practical significance and a very broad application prospect. DETAILED DESCRIPTION

[0081] The present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0082] The composition of the embodiment of the present invention is shown in Table 1, and the rest includes Fe and other inevitable impurities. The composite material of the rolled composite steel plate in the embodiment and the comparative example is described by taking austenitic stainless steel as an example. The manufacturing process parameters of the embodiment of the present invention are shown in Table 2.

[0083] The manufacturing method of the embodiment of the present invention comprises the following steps:

[0084] 1) Smelting and casting: smelting and continuous casting are carried out according to the chemical composition shown in Table 1 to obtain slabs; the smelting equipment is a 500Kg vacuum induction furnace. First, 420kg of industrial pure iron is added to the vacuum induction furnace. According to the alloy composition ratio of the steel, a certain amount of CaO is added with the furnace (the added CaO is used for slag making during smelting); vacuum is drawn, and smelting is carried out at a vacuum degree of about 25Pa at the lowest. Argon gas is required for atmosphere protection during the smelting process; after the pure iron is melted, deoxidizers Si+Mn and Al are added in sequence for pre-deoxidation, and according to the online monitoring results of the molten steel composition, the amount of deoxidizer added is finely adjusted and the oxygen level of free oxygen in the molten steel is controlled to be 0.0020% to 0.0075%, and then an appropriate amount of Ti is added for final deoxidation; alloys such as Nb, Cr, and Mo are added for alloying treatment, and finally B is added; casting is carried out by the top pouring method to cast into a cast billet;

[0085] 2) Assembling, surface treatment is performed on the base carbon steel ingot and the composite stainless steel ingot, the roughness of the butt surface of the two materials is ≤2.0Ra, and after surface inspection, it is ensured that there are no surface defects such as oil stains, slag inclusions, cracks, etc.; the base carbon steel ingot and the composite stainless steel ingot are superimposed to form a composite slab; the composite slab is welded around and then vacuumed, with a vacuum degree of 8 to 60Pa;

[0086] 3) rolling, heating the composite slab at 1080-1250°C, and then performing two-stage rolling, the total cumulative rolling reduction rate is not less than 80%, the total rolling reduction rate of the slab in the first stage is not less than 60%, the total rolling reduction rate in the second stage is not less than 20%, the last pass reduction rate is 8-18%, and the final rolling temperature is above 880°C;

[0087] 4) Heat treatment, quenching and tempering the rolled composite steel plate; quenching the composite steel plate, the quenching temperature is 945-985°C, the quenching holding time T1 is 1-1.2H, and after the holding is completed, the composite steel plate is taken out of the furnace and water-cooled to room temperature; then tempering treatment is performed, the tempering temperature is 690-735°C, the tempering holding time T2 is 1-1.5H, and air cooling is performed after taking out of the furnace.

[0088] In the present invention, the chemical composition design and related processes of the composite steel plates of Examples 1 to 8 all meet the design specification requirements of the present invention.

[0089] Accordingly, the composite steel plates of Comparative Examples 1 to 5 are manufactured using the same process steps as Example 1, except that: the alloy element content of the base carbon steel of Comparative Examples 1 to 4 exceeds the design range, and the alloy range of Comparative Example 5 is still within the design range, but in the smelting and casting operations of the above step 1), the order of adding deoxidizers and the order of adding B alloys in Comparative Examples 1 to 5 are different; the heat treatment and tempering processes are different.

[0090] Electrolytic samples were taken from the carbon steel substrate material and the composite stainless steel side of the composite interface of the composite steel plates of Examples 1 to 8 of the present invention and the control rolled composite steel plates of Comparative Examples 1 to 5. The MC precipitated phases in the substrate carbon steel and the composite stainless steel were extracted by electrolytic extraction, and the precipitated phases in different scale ranges were separated by filter membranes of different particle sizes; the particle size distribution of the precipitated phases was detected by a laser particle size analyzer, and the image analysis software was used to finally confirm the number and size distribution range of the MC precipitated phases (M represents one or more of Nb, Ti, Cr, and Mo) in the steel plates of each embodiment and comparative example, and finally the data obtained by observation and analysis were listed in Table 3 (substrate material) and Table 4 (composite material at the interface, i.e., transition layer).

[0091] As can be seen from Table 3, the total number of precipitated phases in the carbon steel material of the rolled composite steel plate substrate of Examples 1 to 8 ranges from 747 to 908, which is much higher than the number of precipitated phases in the carbon steel material of the substrate of Comparative Examples 1-5, which is 467 to 547. This indicates that after the implementation of the technical solution of the present invention, a larger number of MC (M is one or more of Cr, Mo, Ti, and Nb) carbide precipitated phases can be formed in the carbon steel material of the substrate of Examples 1 to 8, thereby ensuring the effect of fixing free carbon in carbon steel by using stable carbides in the carbon steel substrate as designed in the technical solution. Moreover, the size of the MC precipitated phases in the carbon steel material of the rolled composite steel plate substrate of Examples 1 to 8 is relatively small, and their main distribution range is 100 to 600 nm. The average major axis length of the MC precipitated phase is less than 400 nm, and the volume density of the MC precipitated phase is greater than 3.0×10 4 Pieces / mm 3 The MC precipitates with a size less than 400nm account for more than 50% of the total MC precipitates. When the precipitates are small in size, they can play a role in pinning the growth of austenite grains to a certain extent, thereby refining the grains and further improving the strength and toughness of the material.

[0092] However, the size of the MC precipitated phase in the carbon steel of the rolled composite steel plate substrate of Comparative Examples 1 to 5 is relatively large, the average major axis length of the MC precipitated phase is greater than 800nm, the size distribution range of the main precipitated phase is above 800nm, and the precipitated phase with a size of 1000nm or more accounts for a relatively high proportion, which has a poor pinning effect on the austenite grains, resulting in a relatively large grain size, affecting the strength and toughness of the steel plate. Since the number of stable precipitated phases formed in the carbon steel materials of Comparative Examples 1 to 5 is small, the fixation of the precipitated phase to the free carbon in the substrate carbon steel is reduced, resulting in a large amount of free carbon segregating to the bonding interface (transition layer), thereby generating a large amount of carbides precipitated from the grain boundaries at the composite material of the bonding interface, reducing the corrosion resistance of the composite material at the bonding interface.

[0093] As shown in Table 4, in the composite material of the composite steel plate near the transition layer of Examples 1 to 8, the number of MC (M is one or more of Cr, Mo, Ti, and Nb) precipitated phases detected is 145 to 176, which is much less than 503 to 544 in Comparative Examples 1 to 5, and the volume density of the MC precipitated phase of the composite material at the interface of Examples 1 to 8 is less than 1×10 4 Pieces / mm 3 ; The volume density of the MC precipitated phase of the composite material at the interface of Comparative Examples 1 to 5 is greater than 1.5×10 4 Pieces / mm 3 This shows that the carbides in the base carbon steel materials of Examples 1 to 8 have a good fixation effect on the free carbon elements in the steel, and the amount of free carbon diffused into the composite material through the bonding interface is small, so the amount of MC formed in the composite material is small. In Comparative Examples 1 to 5, since the carbide precipitation phase in the base carbon steel material has a poor effect of fixing the carbon element, the carbon element in the carbon steel material diffuses into the composite material through the bonding interface in large quantities, resulting in a large amount of carbides in the corresponding composite material, and the volume density is greater than 1.5×10 4 Pieces / mm 3 At the same time, it can be seen from Table 4 that in the composite materials at the bonding interface of Examples 1 to 7, the average major axis length of the MC precipitates is less than 700nm, and the MC precipitates with a size less than 700nm account for more than 50% of the total MC precipitates; correspondingly, the average size of the MC precipitates obtained in the comparative example is greater than 900nm. This further illustrates that the carbides in Examples 1 to 8 have a much better fixation effect on free carbon than Comparative Examples 1 to 5.

[0094] After analyzing the carbide precipitation phases of the steel plates for high temperature equipment of Examples 1 to 8 and the comparative steel plates of Comparative Examples 1 to 5, the mechanical properties and corrosion resistance of the steel plates of Examples 1 to 8 and Comparative Examples 1 to 5 were also tested. The test results are shown in Table 5.

[0095] As shown in Table 5, the yield strength of the composite steel plate substrate of the present invention is ≥455MPa, the tensile strength is ≥535MPa, the cross-sectional shrinkage is ≥65%, the elongation is ≥18%, the -40°C impact absorption energy is ≥120J, and the -60°C impact absorption capacity is ≥70J. The shear strength of the composite steel plate is ≥330MPa.

[0096] The yield strength and tensile strength of the carbon steel substrate of the comparative example are lower than those of the embodiment. The main reason is that the smelting process, alloy addition sequence and heat treatment process of the carbon steel of the comparative example substrate are different from those of the embodiment, so that the hardenability of the B element in the comparative example steel cannot be fully exerted, and the precipitation phases in the steel are different, which have different effects on the microstructure of the steel plate. The surface microstructure of the composite steel plate substrate of the present invention is 90-95% bainite + and 5-10% martensite + MC precipitation phases, and the central microstructure of the substrate is 90-95% bainite (B) and 0-5% martensite (M) structure + 0-5% ferrite (F) structure. The microstructure ratio of the carbon steel material in the comparative example is obviously different from that of the embodiment, in which the ratio of bainite and martensite decreases more, and the ratio of ferrite increases, which will also affect the strength of the steel plate.

[0097] In addition, a large number of smaller precipitated phases in the carbon steel substrates of Examples 1 to 8 further refine the austenite grains. The grain size of the carbon steel substrate of the examples is not less than 7.5, while the grain size of the carbon steel substrate in the comparative example is in the range of 5 to 5.5. It can be seen that the embodiments according to the technical scheme of the present invention give full play to the effect of the precipitated phase pinning austenite and refining the grains, which plays a certain role in improving the strength and toughness of the steel plate.

[0098] The composite stainless steel at the interface of the rolled composite steel plates of the embodiment and the comparative example was subjected to corrosion test according to ASTM A262 practice E method, and the test results are shown in Table 6. From the results, it can be seen that the stainless steel at the interface of the rolled composite steel plate prepared according to the requirements of the present invention has excellent corrosion resistance. Therefore, the corrosion resistance of the composite stainless steel plates of each embodiment in the composite steel plates of Examples 1 to 8 is far superior to that of Comparative Examples 1 to 5.

[0099] In summary, the composite steel plate for high-temperature equipment suitable for working temperature of 450-530°C described in the present invention can be optimized by component design and production process, especially by controlling the type of deoxidizer, deoxidation sequence and the amount of deoxidizer added in the steel smelting process, adding B element in a timely and appropriate amount, and then coordinating other production processes, to generate a large number of dispersed nano-scale MC (M represents one or more of Cr, Mo, Nb, Ti) precipitation phases in the substrate steel, and these nano-scale MC precipitation phases can fix the free carbon elements in the substrate carbon steel, thereby avoiding the large-scale diffusion of these carbon elements to the bonding interface, resulting in the formation of a large number of carbide precipitation phases in the stainless steel, resulting in the decrease of the corrosion resistance of the stainless steel. Therefore, the use of the technical solution of the present invention can ensure the strength and toughness of the carbon steel substrate, and at the same time can greatly improve the corrosion resistance of the rolled composite steel plate, and ensure the intrinsic safety performance of the rolled composite steel plate when it is in high temperature and long-term service.

[0100] In addition, it should be noted that the combination of the various technical features in the present invention is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0101] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

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Claims

1. A corrosion-resistant rolled composite steel plate for high-temperature equipment, comprising a substrate, a composite layer and a transition layer between the substrate and the composite layer; the substrate components are as follows by weight: C: 0.08% to 0.18%, Si: 0.01% to 0.6%, Mn: 0.30% to 0.70%, Ti: 0.009% to 0.015%, acid-soluble Als: 0.010% to 0.015%, Nb: 0.0010% to 0.050%, Cr: 1.85% to 3.85%, Mo: 0.5% to 1.55%, B: 0.0007% to 0.0050%, N: 0.0025% to 0.0050%, P≤0.010%, S≤0.010%, O≤0.004%, and the balance includes Fe and other inevitable impurities; The surface microstructure of the composite steel plate substrate is 90-95% bainite + 5-10% martensite + MC precipitation phase, and the central microstructure of the substrate is 90-95% bainite + 0-5% martensite + 0-5% ferrite + MC precipitation phase; wherein, M represents one or more of Cr, Mo, Nb, and Ti, the average major axis length of the MC precipitate phase is less than 400 nm, and the volume density of the MC precipitate phase with a major axis length less than 400 nm is greater than 3.0×10 4 Pieces / mm 3 ; The composite steel plate is made of stainless steel, and its microstructure contains MC precipitated phase; wherein M represents one or more of Cr, Mo, Nb, and Ti, and the average major axis length of the MC precipitated phase is less than 700 nm, and the volume density of the MC precipitated phase is less than 1.0×10 4 Pieces / mm 3 ; Preferably, the stainless steel is austenitic stainless steel, ferritic stainless steel, duplex stainless steel or super stainless steel.

2. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, characterized in that: The composite steel plate substrate also contains at least one of the following chemical elements: 0<Ca≤0.0055%, 0<Ni≤0.65%, 0<Cu≤0.55%.

3. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1 or 2, characterized in that: The balance of the composite steel plate base material components is Fe and other inevitable impurities.

4. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, 2 or 3, characterized in that: In the composite steel plate substrate, the MC precipitated phases with a major axis length of less than 400 nm account for more than 50% of the total MC precipitated phases.

5. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, 2, 3 or 4, characterized in that: In the composite steel plate, the MC precipitated phases with a major axis length of less than 700 nm account for more than 50% of the total MC precipitated phases.

6. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, 2, 3, 4 or 5, characterized in that: The microstructure of the composite steel plate layer also contains a very small amount of σ phase, and the proportion of σ phase is ≤1.5%; preferably, the proportion of σ phase near the transition layer, ie, the bonding interface, is ≤0.5%.

7. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, 2, 3, 4, 5 or 6, characterized in that: The thickness of the composite steel plate substrate is ≥6 mm, and the thickness of the composite layer is ≥2 mm; preferably, the thickness of the transition layer is ≤250 μm.

8. The corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 1, 2, 3, 4, 5, 6 or 7, characterized in that: The yield strength of the rolled composite steel plate substrate is ≥455MPa, the tensile strength is ≥535MPa, the cross-sectional shrinkage is ≥65%, the elongation is ≥18%, the -40°C impact absorption energy is ≥120J, and the -60°C impact absorption capacity is ≥70J; the substrate grain size is not less than grade 7.0; and the shear strength of the composite steel plate is ≥330MPa.

9. The method for manufacturing a corrosion-resistant rolled composite steel plate for high-temperature equipment according to any one of claims 1 to 8, characterized in that: The steps include: 1) Smelting and casting, preparation of base material and composite casting billet According to the composition of claim 1, 2 or 3, the base material ingot is smelted and cast, and deoxidizers Si+Mn, Al and Ti alloys are sequentially added to the molten steel during the smelting process for deoxidation, wherein Si+Mn and Al are first added for pre-deoxidation, and the oxygen level of the molten steel is 0.0020% to 0.0075% after the pre-deoxidation, and then Ti is added for final deoxidation; after the deoxidation, B element is added, and then other alloys are added, and after homogenization, casting is performed using the top pouring method; at the same time, a stainless steel composite ingot is obtained; 2) Assembly The substrate and the composite casting blank are subjected to surface treatment, and then stacked, and the four sides of the stacked composite blank are welded and sealed, vacuumed, and sealed again; preferably, after vacuuming, the vacuum degree is 8 to 60 Pa; 3) Composite slab rolling The composite slab is heated to 1080-1250°C, and then rolled in two stages, the total reduction rate of the slab in the first stage is not less than 60%, the total reduction rate in the second stage is not less than 20%, the reduction rate of the last pass is 8-18%, and the total cumulative reduction rate of the two-stage rolling is not less than 80%; the final rolling temperature is above 880°C; 4) Heat treatment: quenching and tempering heat treatment of the composite steel plate.

10. The method for manufacturing the corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 9, characterized in that: In step 2), the surfaces of the substrate and the composite ingot are processed to ensure that there are no obvious surface defects such as oil stains, slag inclusions, cracks, etc. on the surface of the ingot, and at the same time, the roughness of the processed surface of the ingot must be no greater than 2.0 Ra.

11. The method for manufacturing the corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 9, wherein: In step 4), the quenching temperature is 945-985°C, the quenching holding time is T1=(1-1.2)H, and after the holding is completed, the steel plate is taken out of the furnace and cooled to room temperature with water; wherein T1 is in min, and H is the thickness of the steel plate in mm.

12. The method for manufacturing the corrosion-resistant rolled composite steel plate for high-temperature equipment according to claim 9 or 11, characterized in that: In step 4), the tempering temperature is 690-735°C, the tempering holding time is T2=(1-1.5)H, and after the holding is completed, the steel is taken out of the furnace and cooled to room temperature with water; wherein T2 is in min, and H is the thickness of the steel plate in mm.

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